Evaluation of a quantitative plasma PCR plate assay for detecting cytomegalovirus infection in marrow transplant recipients

Characterization of cytotoxic function of CMV-pp65-specific CD8+ T-lymphocytes identified by HLA tetramers in recipients and donors of stem-cell transplants

BACKGROUND

Human cytomegalovirus (CMV) is a ubiquitous herpesvirus that is an important complication of bone marrow and allogeneic stem-cell transplant (HSCT). CD8 T-lymphocytes have an important role in immunity against CMV, but correlation between antigen-specific subpopulations of these cells and protection are still unclear.

METHODS

Flow analysis with fluorescently-conjugated human leukocyte antigen (HLA) class I tetramers (Tet) was used to investigate levels of CMV-specific CD8 T-lymphocytes in peripheral blood monocyte cells (PBMC) samples from HSCT donors and recipients and their ability to produce interferon (IFN)-gamma on stimulation with either CMV antigenic peptide or nonspecific mitogenic stimulation. Chromium release assays were used to evaluate ex vivo CMV-specific cytotoxicity associated with the PBMC samples.

RESULTS

Use of Tet in conjunction with fluorescently conjugated anti-T-cell receptor (TCR) beta-chain variable (Vbeta) monoclonal antibodies indicated that the Vbeta repertoires associated with Tet cells seen in two HSCT recipients were similar to the Vbeta repertoires of the Tet cells in their HSCT donors. Significant ex vivo cytotoxicity against peptide-loaded targets was measured from several recipient samples after transplant. However, PBMC from the HSCT donors, even when containing populations of CMV-specific Tet cells capable of secreting IFN-gamma in response to peptide stimulation, possessed no ex vivo CMV-specific cytotoxicity.

CONCLUSIONS

We hypothesize that in the setting of the reconstituting immune system of HSCT recipients, CMV reactivation may stimulate a functional change in CMV-specific CD8 T-lymphocytes, rendering them able to directly lyse target cells presenting CMV antigens without in vitro stimulation. These findings have important implications for development of vaccines designed to induce protective cellular immunity to CMV in transplant recipients.

Randomized, placebo-controlled, double-blind study of a cytomegalovirus-specific monoclonal antibody (MSL-109) for prevention of cytomegalovirus infection after allogeneic hematopoietic stem cell transplantation

MSL-109 is a monoclonal antibody specific to the cytomegalovirus (CMV) glycoprotein H with high neutralizing capacity. In a prospective, randomized, double-blind study, allogeneic hematopoietic stem cell transplantation (HSCT) recipients with positive donor and/or recipient serology for CMV before transplantation received either 60 mg/kg MSL-109 (n = 59), 15 mg/kg MSL-109 (n = 60), or placebo (n = 60) intravenously every 2 weeks from day -1 until day 84 after transplantation. CMV pp65 antigenemia, CMV-DNA load in plasma, and viremia by culture were tested weekly. Primary end points were development of pp65 antigenemia at any level and/or viremia for which ganciclovir was given. There was no statistically significant difference in CMV pp65 antigenemia or viremia among patients in the 60-mg group (pp65 antigenemia, 47%; viremia, 15%), the 15-mg group (52%; 23%), and the placebo group (45%; 17%). There was also no difference in maximum levels of pp65 antigenemia, time to clearance of pp65 antigenemia after start of ganciclovir, CMV disease, invasive bacterial and fungal infections, time to neutrophil and platelet engraftment, acute graft-versus-host disease, days of hospitalization, and overall survival rate among the 3 groups. However, a subgroup analysis of CMV-seronegative recipients with a seropositive donor (D+/R-) showed a transiently improved survival rate by day 100 in MSL-109 recipients (mortality: 60-mg group, 1/13; 15-mg group, 1/12; placebo group, 6/10 [P = .02 for 60-mg versus placebo groups; P = .08 for 15-mg versus placebo groups]); by the end of follow-up, the difference was no longer statistically significant. The improved survival rate in D+/R- patients could not be attributed to a reduction in CMV disease; however, MSL-109 was associated with improved platelet engraftment and less grade III to IV acute graft-versus-host disease in this subgroup. In a subgroup analysis of CMV-seropositive recipients of MSL-109 (D+/R+ and D-/R+), overall mortality was increased compared to that of the placebo group (P = .12 for the 60-mg versus placebo groups, P = .05 for the 15-mg versus placebo groups, and P = .04 for the dose levels combined versus placebo). MSL-109 was well tolerated and no immune response to the drug was observed. Thus, MSL-109 was safe but did not reduce CMV infection in allogeneic HSCT recipients. The transient survival advantage seen early after transplantation in CMV D+/R- patients and the negative effect on survival in seropositive patients remain unexplained. Thus, there is no evidence that MSL-109 is beneficial in CMV-seropositive HSCT recipients.

Increased human cytomegalovirus (HCMV) DNA load in peripheral blood leukocytes after lung transplantation correlates with HCMV pneumonitis

BACKGROUND

Human cytomegalovirus (HCMV) reactivation and disease remain relatively common in lung transplant recipients (LTR) despite the use of ganciclovir prophylaxis protocols for all HCMV at-risk patients. The specific aims of this study were to (1) describe the HCMV DNA viral load in the peripheral blood leukocytes (PBL) of a cohort of LTR during the first 6 months after lung transplantation; (2) prospectively determine whether HCMV DNA viral load predicts episodes of HCMV pneumonitis in LTR; and (3) study the effect of ganciclovir on HCMV viral load.

METHODS

Competitive polymerase chain reaction using an internal standard and fluorometric detection were used to quantitate HCMV DNA in the PBL of a cohort of 26 LTR monthly for the first 6 months after transplantation (145 samples). All patients were treated with standard triple immunosuppression, and ganciclovir prophylaxis was given to all at-risk LTR (donor or recipient HCMV seropositive) for at least 8 weeks after transplantation.

RESULTS

Thirteen episodes of histopathologically proven HCMV pneumonitis in nine subjects occurred during follow-up with a wide intra- and intersubject variation in the HCMV DNA PBL levels. HCMV detection had a sensitivity of 92% and specificity of 76% for HCMV pneumonitis (negative likelihood ratio, 9.5), whereas greater than 10-fold increases in HCMV DNA load had a specificity of 93% and sensitivity of 67% (positive likelihood ratio, 11). HCMV DNA detection had an adjusted odds ratio for HCMV pneumonitis of 107 (95% confidence interval, 14-821; P<0.005). In those with detectable HCMV DNA in PBL (n=44), HCMV DNA levels were 4.4 (95% confidence interval, 1.2-16.8) times higher in those with HCMV pneumonitis than in those without HCMV pneumonitis. Although ganciclovir treatment was very effective in treating HCMV pneumonitis and suppressing HCMV DNA levels, thrice weekly ganciclovir prophylaxis only partially controlled HCMV DNA levels and did not eliminate HCMV pneumonitis risk as three patients developed HCMV pneumonitis while on this regimen.

CONCLUSIONS

HCMV DNA detection, absolute levels, and relative change from baseline in the PBL of LTR correlate with HCMV pneumonitis episodes and may be a useful intermediate outcome measure of the efficacy of ganciclovir prophylaxis and treatment strategies.

Infrequent occurrence of natural mutations in the pp65(495-503) epitope sequence presented by the HLA A*0201 allele among human cytomegalovirus isolates

To determine if mutations of an immunodominant HLA-restricted cytomegalovirus (CMV) peptide sequence occur in nature, the sequence corresponding to the HLA A*0201-specific peptide CMVpp65(495-503) was determined in 50 human CMV isolates. Rare mutations were detected; 6 of 50 were silent mutations at the amino terminus of the peptide, while 3 of 50 were mutations of the native methionine residue to isoleucine (M499I). The observed M499I mutation in three isolates decreased cytolytic targeting.

Enhanced analytical sensitivity of a quantitative PCR for CMV using a modified nucleic-acid extraction procedure

Accurate and rapid diagnosis of CMV disease in immunocompromised individuals remains a challenge. Quantitative polymerase chain reaction (QPCR) methods for detection of CMV in peripheral blood mononuclear cells (PBMC) have improved the positive and negative predictive value of PCR for diagnosis of CMV disease. However, detection of CMV in plasma has demonstrated a lower negative predictive value for plasma as compared with PBMC. To enhance the sensitivity of the QPCR assay for plasma specimens, plasma samples were centrifuged before nucleic-acid extraction and the extracted DNA resolubilized in reduced volume. Optimization of the nucleic-acid extraction focused on decreasing or eliminating the presence of inhibitors in the pelleted plasma. Quantitation was achieved by co-amplifying an internal quantitative standard (IS) with the same primer sequences as CMV. PCR products were detected by hybridization in a 96-well microtiter plate coated with a CMV or IS specific probe. The precision of the QPCR assay for samples prepared from untreated and from pelleted plasma was then assessed. The coefficient of variation for both types of samples was almost identical and the magnitude of the coefficient of variations was reduced by a factor of ten if the data were log transformed. Linearity of the QPCR assay extended over a 3.3-log range for both types of samples but the range of linearity for pelleted plasma was 20 to 40,000 viral copies/ml (vc/ml) in contrast to 300 to 400,000 vc/ml for plasma. Thus, centrifugation of plasma before nucleic-acid extraction and resuspension of extracted CMV DNA in reduced volume enhanced the analytical sensitivity approximately tenfold over the dynamic range of the assay.

Clinical utility of a quantitative polymerase chain reaction for diagnosis of cytomegalovirus disease in solid organ transplant patients

BACKGROUND

Accurate and rapid diagnosis of human cytomegalovirus (HCMV) disease in solid organ transplant patients remains a challenge. We evaluated the clinical utility of a quantitative polymerase chain reaction (QPCR) method to diagnose transplant patients with HCMV disease.

METHODS

A total of 429 plasma samples from 121 solid organ transplant patients were prospectively collected and evaluated for HCMV using a QPCR assay. To enhance the sensitivity of the QPCR assay, plasma samples were centrifuged in a manner designed to concentrate the virions before nucleic acid extraction. Quantitation was achieved by co-amplifying an internal quantitative standard (IS) that contained the same primer sequences as for HCMV. Polymerase chain reaction products were detected by hybridization to 96-well microtiter plates coated with either a HCMV- or an IS-specific probe.

RESULTS

A total of 103 patients had all samples negative by QPCR. None of the 103 patients developed HCMV disease during the study. In contrast, 18 patients showed at least 1 sample positive by the QPCR assay, but only 8 of these developed HCMV disease. The mean viral load value for patients without HCMV disease was 93 viral copies (vc) per ml of plasma (range: 35-325 vc/ml plasma) and for the 8 patients with HCMV disease was 67,686 vc/ml plasma (range: 167-1,325,000 vc/ml plasma) (P<0.001). Using a cut-off value of 100 vc/ml plasma and clinical diagnosis of HCMV disease, the QPCR assay showed a sensitivity of 100% and specificity of 99.1%.

CONCLUSION

HCMV viral load may be useful in the diagnosis of HCMV disease in solid organ transplant patients.

A highly sensitive assay for detection and quantitation of human cytomegalovirus DNA in serum and plasma by PCR and electrochemiluminescence

We describe a diagnostic PCR assay (D-PCR) and a quantitative PCR assay (Q-PCR) for the detection of human cytomegalovirus (CMV) in plasma and serum. In the D-PCR, DNA was purified from plasma or serum together with internal control (IC) DNA, which monitored both DNA extraction efficiency and PCR efficiency. DNA was subjected to PCR with a single primer pair, and the amount of PCR products was determined by electrochemiluminescence (ECL) in the QPCR System 5000 (Perkin-Elmer) after hybridization with Tris (2,2'-bipyridine) ruthenium (II) chelate-labeled probes. The lower limit of sensitivity of the D-PCR was reached at about 25 CMV particles/ml. Even with extremely low DNA inputs (four molecules of IC DNA/200 microl of plasma), very high yields (near 100%) were reached. DNA extracted from specimens that were CMV positive by the D-PCR was subsequently used in the Q-PCR, which was similar to the D-PCR. The viral load was calculated directly from the ratio of CMV and IC signals obtained by ECL. The Q-PCR assay is quantitative in the range of 100 to 150,000 copies of CMV/ml, independent of the anticoagulant. Interassay variation, intra-assay variation, and interspecimen variation were about 25%, suggesting that the Q-PCR will reliably detect fourfold differences in viral load. Comparison of paired serum and plasma specimens from CMV-infected individuals showed that serum CMV loads were frequently more than 10-fold lower than plasma CMV loads.

Utility of cytomegalovirus viral load in renal transplant patients in Argentina

BACKGROUND

Cytomegalovirus (CMV) is the most prevalent viral disease in solid organ transplantation. Detection of CMV DNA in peripheral blood mononuclear cells (PBMC) by polymerase chain reaction (PCR) frequently occurs in renal allograft recipients, yielding false positive results in seropositive patients free of CMV disease. We evaluated the clinical utility of a quantitative PCR-enzyme-linked immunosorbent assay (ELISA) for identifying patients with CMV disease.

METHODS

Three hundred and fifty samples from 65 consecutive renal transplant recipients were studied. DNA was extracted from PBMC weekly up to the day of discharge and after any further admission. Samples were tested by a qualitative PCR method, and all positive samples were further studied by a quantitative PCR-ELISA method. The quantitative PCR-ELISA method used an internal standard (IS) that contained the primer sequences used in the qualitative CMV PCR. Detection and quantification was performed in 96-well plates coated with IS or CMV specific probes.

RESULTS

Forty-one of 65 patients (63.1%) showed positive results by the qualitative PCR, but only 8 of these patients were diagnosed with CMV disease. Positive samples were re-analyzed by the quantitative assay. The 8 patients with CMV disease had a mean CMV viral load of 1,438+/-687 viral copies (VC)/10(6) PBMC, and the 33 without CMV disease had a mean value of 219.6+/-117.2 VC/10(6) PBMC (P<0.01). None of the 33 patients without CMV disease had viral loads higher than 500 VC/10(6) PBMC. Using 500 VC/10(6) PBMC as a cut-off value for CMV disease, the quantitative PCR showed a sensitivity and specificity of 100% compare to clinical diagnosis.

CONCLUSION

CMV viral load may be useful in the diagnosis of CMV disease in renal transplant patients.

Quantitative measurement of equine cytokine mRNA expression by polymerase chain reaction using target-specific standard curves

Quantification of cytokine mRNA using reverse transcription coupled with the polymerase chain reaction (RT-PCR) has become a corner stone of the study of cytokine regulation. Quantitative competitive RT-PCR (QCRT-PCR) is commonly accepted as a reliable method for quantifying differences in mRNA levels but is both labor- and reagent-intensive. A noncompetitive polymerase chain reaction method that utilizes cytokine-specific, plasmid-derived, standard curves was developed for the quantification of equine cytokine mRNA. The assay can be performed on minute samples of cellular material, utilizes sequences identical to wild-type for the generation of standard curves, is technically facile, less reagent-and labor-intensive than competitive methods, easily accommodates high sample throughput without the use of radioactive labels, and generates replicate samples to allow statistical analysis of the data. We demonstrate the utility of the assay, which is easily adapted to any cloned mRNA sequence, using equine interleukin-10 (IL-10). Both IL-10 and beta-actin cDNA were amplified in triplicate PCR reactions from oligo-dT primed RT reactions. Dilutions of plasmid DNA encoding the respective sequence, equine IL-10 or beta-actin, were also amplified in triplicate reactions in the same run. Beta-actin cycling parameters were modified to maintain the amplification in its exponential phase by decreasing both cycle number and cDNA volume relative to the parameters used for cytokine amplification. Following amplification, aliquots of the PCR reactions were hybridized with sequence-specific tris (2,2'-bipyridine) ruthenium II chelate labeled oligonucleotide probes and quantified using the QPCR System 5000. Plasmid derived values were used to generate a standard curve for the interpolation of mRNA content in unknown cDNA samples. Beta-actin values were used to derive a factor for the relative normalization of differences among cDNA samples that are inherent in the RNA extraction and RT steps. This assay resolves at least 2-fold differences in message, is reproducible, and has a dynamic range on the order of 3 logs.

Detection of PCR-amplified fungal DNA by using a PCR-ELISA system

In order to speed up and standardize polymerase chain reaction (PCR)-based detection of medically important fungi in clinical samples we established a combination of commercially available kits for DNA extraction, PCR amplification and detection of the amplicons. The PCR plate assay proved to be as sensitive and specific as our previously published assay (5 cfu ml(-1) blood). Moreover, in a selected group of patients, all patients with proven and probable invasive fungal infection were found to be PCR-positive. Thus the PCR plate assay was found to be a sensitive, technically simplified and standardized method with potential for adaptation to automation.

The clinical utility of viral quantitation using molecular methods

BACKGROUND

The quantitation of viral nucleic acids in biological fluids has become increasingly desirable over the past several years. To this end, a number of quantitative molecular procedures have been developed.

OBJECTIVES

The objective was to review the current literature on the molecular techniques used in the quantitation of viral nucleic acids and to assess the appropriateness of these methods for clinical use.

RESULTS

Assays involving both target and signal amplification are now available for the accurate and precise quantitation of viral burden in infected patients. These methods include quantitative polymerase chain reaction (PCR), branched chain signal amplification (bDNA), nucleic acid sequence-based amplification (NASBA) and the SHARP signal and hybrid capture systems. Our understanding of the natural history and pathogenesis of viruses such as the human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), cytomegalovirus (CMV) and Epstein-Barr virus (EBV) may be greatly facilitated by accurate determinations of viral and infected cell burden. Quantitation of viral load in infected individuals may also be useful to assess disease progression, monitor the efficacy of therapy and to predict treatment failure and the emergence of drug-resistant viruses.

CONCLUSION

Precise, accurate and reproducible quantitation of viral load is now feasible. Molecular assays for viral quantitation should have a considerable impact on medical research and clinical care.

Evaluation of Murex CMV DNA hybrid capture assay for detection and quantitation of cytomegalovirus infection in patients following allogeneic stem cell transplantation

Murex hybrid capture DNA assay (HCS) is a solution hybridization antibody capture assay for detection and quantitation of cytomegalovirus (CMV) DNA in leukocytes. To determine whether CMV HCS is sensitive enough to initiate and monitor antiviral therapy after allogeneic stem cell transplantation (SCT), 51 consecutive SCT recipients were prospectively screened for the appearance of CMV infection by HCS, PCR, and culture assays from blood samples. Preemptive antiviral therapy was initiated after the second positive PCR result in all patients, as previously reported, and HCS was not considered for clinical decision making. A total of 417 samples were analyzed. Of these, 21 samples were found to be positive by PCR and HCS, 88 samples were PCR positive but HCS negative, and 308 were negative by both assays. Concordance of results between PCR and HCS and between HCS and blood culture was observed in 78.9 and 95.9% of the samples assayed, respectively. PCR was found to be more sensitive than HCS, and HCS was more sensitive than the blood culture assay (P < 0.0001). Four patients with symptomatic CMV infection were PCR positive prior to the onset of CMV-related symptoms, whereas HCS detected CMV DNA in three patients prior to and one at onset of CMV disease. The numbers of genomes per milliliter of blood were higher in patients with symptomatic CMV infection than in those with asymptomatic CMV infection (P = 0.06). None of the HCS-negative patients developed CMV disease. Thus, all patients with CMV disease were correctly identified by HCS; however, the lower sensitivity limit of the HCS assay may still be insufficient to allow diagnosis of CMV infection early enough to prevent CMV disease in patients following allogeneic SCT.